1. Field of the Invention
The present invention relates to an organic EL display device which performs display using self-luminous EL (electroluminescence) elements as pixels which are arranged in a matrix form and, more specifically, to an organic EL display device suitable for reducing variations in luminance among pixels.
2. Description of the Related Art
Display devices employing organic EL elements have characteristics, not realized by LCDs (liquid crystal display devices), in that the organic EL elements require no backlights because they are self-luminous elements and thus suitable for reducing power consumption. Those display devices further have fast response and wide viewing angle characteristics, and also have advantages that they are adaptable to flexible applications and so on since the elements themselves are solid.
Possible systems of driving the organic EL display device include, similarly to LCD, PM (passive matrix) drive and AM (active matrix) drive, and the AM system is mainstream in which a thin film transistor (TFT) is provided for each pixel to individually control the pixel. This also allows for higher definition, longer life, and much lower power consumption.
Incidentally, to control the light emission of pixels of the organic EL display device without variations, it is necessary to make current values of the pixels identical to each other with respect to a certain image signal. This point is particularly important for a system in which the pixels are supplied with the image signal in an analog signal and are caused to perform intermediate light emission in accordance with its analog value. Examples of the organic EL display device aimed at reducing unevenness of luminance on the precondition described above include, for example, one described in the following Patent Document 1.
[Patent Document 1] Japanese Patent Laid-Open Application No. 2002-91377
In the display device disclosed in the above document, a configuration is employed which negatively feeds back pixel currents such that the current match an image signal. Accordingly, even if there are variations in input voltage versus output current characteristics of current controller circuits, the variations are absorbed so that current values among pixels identical to a certain image signal are obtained. However, necessarily, an error amplifier circuit required for negative feedback needs to be built in for each pixel, and therefore it is considered that the display device has a disadvantage in the aperture rate of display (rate of net area of light emitter to surface area).